Date of Award
Master of Science
The marsh rice rat (Oryzomys palustris) is a semi-aquatic rodent classified as state-threatened in Illinois due to historical wetland loss coupled with being on the northern periphery of its range. The most recent survey for this species in Illinois occurred in 1988, and this study reassessed its status and distribution. From 2007 to 2009, I used live traps to sample for rice rats at previously occupied and random wetland-dominated sites in 5 southern Illinois watersheds. I captured 132 individual rice rats 192 times in 13,248 trap nights. Capture success was 15.10 captures/1,000 trap nights. I detected rice rats within 3 of 5 watersheds, 16 of 48 sites, and 5 new locations. Most rice rats were captured in permanent or semi-permanent emergent wetlands and rice rat occurrence was strongly related with coal mine-associated wetlands. I collected microhabitat measurements at 10% of trap locations and recorded landcover types within and around sites. I analyzed data using t-tests, logistic regression, and occupancy modeling. Percent herbaceous cover and percent visual obstruction (0.0-0.5m) positively influenced rice rat occurrence and were among the most important microhabitat models. The best model in the candidate set of landcover variables included proportion of upland grass in areas surrounding wetlands as a predictor of rice rat occurrence. I believe insufficient evidence exists to warrant removal of the threatened status of the marsh rice rat. However, current management practices, such as wetland restoration, grassland restoration, and mowing of roadside ditches, likely benefit rice rat populations. Slight modification of these management activities may facilitate the eventual delisting of marsh rice rats.
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